It might be a similar error to something I saw in other extensions, but I never found which extension was causing the issue in the first place.
This can happen if a middleware reads the list of uploaded files and doesn't rewind the stream, which then causes the controller to fail.
Alternatively, maybe your webserver is not including the uploaded file in the request at all, maybe because it's too big, or because of some firewall rules.
Is this happening for any file on any user? Did it work previously? What kind of hosting and webserver are you using?
